Solar Cycle 24 Group I

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Group I Session 1 What are active region coronal loops?

Ignacio Urgate-Urra

Future active region future obs hinode etc...Thurs?

First question: Where is the pinot noir?!

What are coronal loops? -Why they reach temp, evolve, structure? -Do they actually reach these values?! -Is there a typical loop? -Common loops? -Do scientists agree? -What do models need from observers?

Helen: Does a loop have to return to the sun? How big? Markus: Don't see loops in open regions? Helen: Should we only be interested in loops or active region as a whole? Markus: Large loops and scaling laws can produce fan like-not closed loops eg TRACE. Hardi: 90% energy goes into flow. Open field lines factor 100 reduced in intensity. (Leer). George: Bigger flows = dark loops.


-Temp structure is time dependent, cooling - etc Helen: are apparent single loops really loops? Do loops cool in the same way? Dynamic loops, flare loops

What temp do they reach - xrt - Ko (09)


Static vs Dynamic Pre-SOHO (Klimchuk 08) Soft xray loops - life times longer than cooling time.

BUT

Dynamic SXR component Transient brightenings - EUV counterparts - xray loops cool to EUV -Tsuneta 94- Shimizu 94 concludes that microflares observed by Yokoh alone can't heat active region corona. Does this rule out Parker nano flares? Need more sensitivity ie XRT. -Microflaring is important even for long lived loop.

Different phases - steady AR, Implusive AR, QS Hardi: Are phyical heating mechanisms in different phases the same steady AR, Implusive AR, QS?

EUV loops -Warm 0.5 < T < 1-3Mk -Over dense -Super hydrostatic scale heights - impulsiveness - TRACE loops densities are higher than hydro equilibrium.

How are EUV loops related to XRT loops? XRT loop lifetimes are longer than cooling times


-There is a subset of loops with T<1Mk -These loops host slow waves

-Coronal rain, thermal non-equilibrium, steady footpoint heating.


STRUCTURING -are loops monolithic? -have we seen elementary strands? -smooth temp and density across loop axis -smooth temp and density across strand axis Markus: loop strands > 1500km are composite Believe individual stands have been observed by trace. Multi stands at same temp would be monolithic very unlikely.

-are they multi-stranded? Warren paper. -Ugarte-Urra 2009 cooling times - individual loops?

Would super high resolution TRACE show fine structures -Fine scale in chromosphere may not necessarily be reproduced in corona due to temp dependence gyroradius etc - Markus, Hardi.

Multi-thermal Filter analysis Spectroscopic analysis - narrow DEM - previous broad DEM (Schmeltz)


Implications for heating -nanoflares - convection - braiding -stress - reconn -PRO: impulsive, explains overdense, multi-strand, broad DEM -CONS: not seen (yet), monolithic loops, no obsrved braiding

- Nano flare storm - narrow DEMs

Hardi: Cons not necessarily cons - Events overlap enough for apparent continuous distribution.

-chromospheric heating - Reconn at chromospheric level - Cross field diffusion more efficient -> coherence - Poss explanation for outflow/waves

- open questions - Coronal heating can explain - upflows chromospheric evaporation - How much dissipation at low heights goes into heating corona - Radiative losses?

-Cons: Hinode no mixed polarity in plage

-Debate shifting to heating localisation


Is there a typical loop - Maybe? Do loop share common properties - No What do models need from obs - need to provide

Need spectroscopic + time dependent properties of multiple loops AR.

Hardi: Need coronal magnetic fields


Session 2 Joint I+C session Coronal loops and the slow solar wind

Scott MacIntosh Into the Corona with CoMP

CoMP 3 lines - 1 corona 2 chromosphere Full stokes vectors Fe XIII

1 hour observations -Static off limb observations in intensity - line width -Doppler movie shows outward propagation of waves. No compressive/intensity signal.

-Phase speeds of 1-4Mm/s -Amp 0.25-0.5 km/s -Power spectra show dominance of 5-min periods. -Deduce observations of coronal Alfven waves.

Time-distance seismology of the corona Tomchzk 07, Tomchzk & McIntosh,08 -Previous analysis insensitive to angles > 65 degrees

Tracking in 2D -Time-Distance time series -Coronal k-omega diagram -Detection of upward and downward waves -greater amplitude of upward waves -Original analysis phase speeds were factor of 2 too large. Now 650 km/s

Aschwanden: Comparison to kink mode intepretation

Question of why line of sight integration does not smooth out observations of these waves?



George Doschek Active Region Flows Observed by EIS

EIS has slit and slot observing modes Long wavelenth band spectrum -About 50% of lines are new - not included in chianti -may be important for irradiance studies -Lines only observed in skylab flares observed routinely with EIS -EIS allows new observations of non-thermal line width -TR & coronal lines are greater than theory predicts - reconn, bulk flow, MHD waves, other?


Non-thermal motions - what is known -Average V vs T is known -Average V with hight about the limb is known in some cases.


XRT continous upflows of plasma in loops -Apparent upflow ~140 km/s -Occur in darker areas of active regions, correlated with non-thermal width -line width and centroid shift correlated

Doschek, 2008 -Temperature structure to the flows -multi flow components, two component flows in line profiles.

General properties of an outflow region -multi component centroid shifts -flow velocity-masking allows outflow regions to be indentified spatially.

Mason: What do more obs of these kind of regions tell us? Doschek: Return statistical sample of observations.

Doschek: Brighter active regions would allow observations in more lines.


Modelling contribution of active regions to heiospheric field. Do EIS upflows flow along oped field lines and contribute to solar wind?

12 may 07 13UT EUVI upflows & EIS Doppler map.

Mass outflow flux -Spicule mass flux 1.7x10^-9 g/cm^2/s -11 Dec 10^-5 g/cm^2/s for Doppler speeds > 12km/s and 1.6x10^-6 g/cm^2/s for Doppler > 30 km/s

Use PF extrapolation combined with Doppler flow to determine flow velocity.

Mason: Are PF extrapolations available. DeRosa: PFSS available in solarsoft. Based on MDI magnetograms. 1 degree resolution. ROI extrapolation available. Peter: Should be careful using these extrapolation - different alpha.

Wrap-up Outflow out of the room!

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